Deobfuscate/Decode Files or Information
Adversaries may use Obfuscated Files or Information to hide artifacts of an intrusion from analysis. They may require separate mechanisms to decode or deobfuscate that information depending on how they intend to use it. Methods for doing that include built-in functionality of malware, Scripting, PowerShell, or by using utilities present on the system.
Another example is using the Windows
copy /b command to reassemble binary fragments into a malicious payload. 
menuPass has used certutil in a macro to decode base64-encoded content contained in a dropper document attached to an email. The group has used
One TYPEFRAME variant decrypts an archive using an RC4 key, then decompresses and installs the decrypted malicious DLL module. Another variant decodes the embedded file by XORing it with the value "0x35".
Identify unnecessary system utilities or potentially malicious software that may be used to deobfuscate or decode files or information, and audit and/or block them by using whitelisting  tools, like AppLocker,   or Software Restriction Policies  where appropriate. 
Detecting the action of deobfuscating or decoding files or information may be difficult depending on the implementation. If the functionality is contained within malware and uses the Windows API, then attempting to detect malicious behavior before or after the action may yield better results than attempting to perform analysis on loaded libraries or API calls. If scripts are used, then collecting the scripts for analysis may be necessary. Perform process and command-line monitoring to detect potentially malicious behavior related to scripts and system utilities such as certutil.
Monitor the execution file paths and command-line arguments for common archive file applications and extensions, such as those for Zip and RAR archive tools, and correlate with other suspicious behavior to reduce false positives from normal user and administrator behavior.
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